As industry has continued to refine and improve production procedures, corresponding requirements have been observed for placing identifying or data related markings upon components of manufactured assemblies. With such marking, the history of a product may be traced throughout the stages of its manufacture. In addition, the marking of components, especially those in complex subassemblies, facilitates replacement and reassembly upon repair. For example, the marking of the constituent components in a transmission enables the repairer to readily substitute worn or otherwise damaged gears or the like with the appropriate replacement parts.
In the recent part, a computer driven dot matrix marking technique has been successfully introduced into the marketplace. Described in U.S. Pat. No. 4,506,999 by Robertson, issued Mar.. 26, 1985, entitled "Program Controlled Pin Matrix Embossing Apparatus", and assigned in common herewith, the marking approach described employs a series of tool steel marker pins which are uniquely driven using a pneumatic floating impact concept to generate man-readable and/or machine readable dot codes. Marketed under the trade designation "PINSTAMP", these devices carry the noted marker pins in a head assembly which is moved in linear fashion relative to the piece being marked to indent a dot or pixel defining permanent message or code into a surface of the marked component. Further, the message characters so created are formed from within a convention pixel matrix rows and columns. The approach enjoys the advantage of providing characters of good legibility as well as permanence. Further, the device provides dot matrix characters of good abrasion resistance, and is advantageously capable of marking upon such surfaces as epoxy coatings. Use of this basic row and column dot matrix character forming device is limited, however, to piece parts which are both accessible and of sizes adequate upon which to form linear character strings.
Robertson, et al, in U.S. Pat. No. 4,808,018, issued Feb. 28, 1989, and assigned in common herewith, describes a dot matrix character impact marking apparatus which is capable of forming messages or arrays of characters within confined regions. With this device, a linear array of marker pins is moved by a carriage in a manner defining an undulating locus of movement. This locus traces the standard row and column matrix within which characters are defined by the pixel position indentations created by the marker pins. The carriage and head containing the marker pins are pivotally driven by a cam to provide vertical movement and by a Geneva mechanism to provide horizontal movement. Pixel positions for the matrices are established by use of a timing disk. Each marking pin within the associated marker head assembly of this portable device is capable of marking more than one complete character for a given traverse of the marker head between its limits of movement. However, use of the impact marking device is also limited to parts with surface geometries suitable for the forming of linear marking arrays.
Robertson, et al., U.S. Pat. No. 5,015,106 issued May 14, 1991 entitled "Marking Apparatus with Multiple Line Capability," assigned in common herewith, describes a dot matrix character impact marking apparatus that advantageously is capable of producing multi-line character arrays of variable size. The multi-line capability is developed through the use of a print head that incorporates two parallel linear arrays of marker pins. An actuator assembly, driven by electric-motor-powered facing cam wheels, urges the marker head assembly along a single plane locus of movement defining a sequence of rows corresponding with the rows of a row-column defined pixel matrix. The locus includes a retrace feature for each row of transverse movement which enhances the quality of character formation. However, this device too is limited to applications wherein a surface of a size sufficient for marking a linear character string is present.
The demonstrated success of the above-noted PINSTAMP based marking device has led to additional demands from the industry for an impact making device capable of forming characters, codes, or messages within a region so confined that a linear array of readable markings would otherwise be limited to only a few characters. Such limited making regions are, for example, encountered with circular workpieces. One approach to marking such circular workpieces has been to form characters on their cylindrically shaped outer edges. However, such techniques are cumbersome and inefficient. For gears, washers, bearing flanges and the like, however, such peripheral marking techniques and marking approaches are barred by the unavailability of a circumferential surface upon which characters may be formed.
Generally, the dot-defined characters for the above systems are formed utilizing a conventional matrix, for example having several parallel, linear rows of five pixels each and five generally perpendicularly disposed parallel columns of seven pixels each. Deviations from this rectangular matrix structure have been considered to potentially detract from the readability of resultant characters.